1. Field of the Invention
The present invention relates to toll restrictors for use in determining whether attempts to complete a trunk call are unrestricted and for preventing the completion of a call having a restricted code.
2. Description of the Prior Art
Toll restrictors are well known in the art, such as toll restrictors which recognize any three digit code. An example of such prior art toll restrictors is disclosed in U.S. Pat. Nos. 3,692,951; 3,736,383; 3,014,989 and 2,916,555. However, these prior art toll restrictors are complex and require a large quantity of relays, such as a cascade arrangement of the type disclosed in U.S. Pat. No. 3,692,951, wherein 120 relays or the equivalent thereof may be required. Such a complex arrangement is costly, inefficient and introduces a greater likelihood of failure due to the large number of components involved. Prior art toll restrictors which are responsive to a three digit code, normally consider each digit in the three digit code separately thus requiring the large number of relays previously mentioned in order to handle all possible combinations. Furthermore, such prior art toll restrictors cannot readily and simply be modified to provide all possible restriction combinations, such as one code in a group of three digit codes having the same first two digits being unrestricted or more than one code in such a group, but less than all, being unrestricted. These disadvantages of the prior art are overcome by the present invention.